The present invention relates to a sewage treatment process and apparatus, and particularly to a process and apparatus for filtering sewage so as to remove organic solids therefrom and provide a substantially pure effluent emanating therefrom in accordance with desired standards.
A common way of filtering sewage is through the use of a so-called and relatively expensive rapid-sand filter. Rapid-sand filters require a substantial amount of land area. They also must be backwashed in order to clean the sand filter material. Further, the backwash water must be treated and handled.
In addition, the rapid-sand filter during heavy solids loading quickly requires backwashing. As a result, during heavy solids loading a rapid-sand filter backwashes for a substantial time period and little filtering actually occurs. Further, rapid-sand filters in the event of a power failure are totally inoperative since the pumps and motors thereof cannot be operated.
Notwithstanding the problems with rapid-sand filters, the rapid-sand filter today is the best known and most used method for filtering sewage so as to provide the desired purification of the effluent emanating therefrom. The rapid-sand filters meet government standards on the degree of solids which are permitted in the effluent emanating from the filter only under ideal operating conditions.
The present invention is directed to a substitute for the rapid-sand filter, and particularly a substitute which does not involve the large land area required by a rapid-sand filter, and does not require backwashing. Thus, the present invention obviously avoids the necessity of treatment of backwash water. Also, the present invention is effective and continuously operates to provide desired effluent during heavy solids loading. Moreover, the present invention is substantially less expensive than the rapid-sand filter and operates even if there is a power failure. Further, not only does the present invention avoid the problems with the rapid-sand filter, but also the method and apparatus of the present invention is a practical and economical way of filtering sewage.
In accordance with the present invention, the sewage is subjected to two filtering treatments, with the filter element in both treatments being a disposable sheetlike filter. The first filtering is a standardizing filter stage. The second is a polishing filter stage. The function of the first treatment is to standardize the particle size delivered to the polishing stage. The polishing stage filters the finer solids and the effluent of the desired quality flows therefrom. In the event of a heavy solids loading, the two-stage filtering is effective to provide a purified effluent without the need for backwashing.
In both filter stages the sewage is deposited on a disposable filter sheet and as the fluid flows through the filter sheet, solid particles are retained on the filter sheet. As the pores of the filter sheet fill up and clog, the sewage forms a pool on the filter sheet. When the pool rises to a predetermined level, a switch is tripped which actuates a filter indexing operation. Specifically, the filter sheet is indexed to expose a clean filter sheet area to the sewage which is the pool.
A portion of the filter sheet is moved out of the pool of sewage during indexing. After a time period, the filter sheet, due to the various indexing operations, is moved through a drying zone. This drying zone is in part defined by a discharge ramp which extends upwardly at an angle to the pool of sewage, (in the order of 25 degrees to the horizontal) and further includes a vertical drop from the end of that discharge ramp. This drying zone is made large enough so as to enable the filter sheet and intercepted solids to be completely dried prior to the need for the filter sheet to be handled for removal from the equipment. The complete drying of the sewage on the filter sheet enables the used filter sheet with the sewage dried thereon to be readily handled. Further, the handling thereof is not obnoxious to workers.
As noted above, the use of the two-filter process of the present invention, i.e., standardizing and then polishing, is necessary in order to obtain a continuous flow of effluent with the desired parts of solids therein from the filtering system under extremely high solids loading. Further, with the present invention, no backwashing is necessary, costs are lower, use area is smaller, and standby power may be available. The present invention is a substantial improvement over the rapid-sand filter.